On Fri, Nov 01, 2024 at 09:47:04AM -0400, Gregory Price wrote:
> Systems with hotplug may provide an advisement value on what the
> memblock size should be. Probe this value when the rest of the
> configuration values are considered.
>
> The new heuristic is as follows
>
> 1) set_memory_block_size_order value if already set (cmdline param)
> 2) minimum block size if memory is less than large block limit
> 3) if no hotplug advice: Max block size if system is bare-metal,
> otherwise use end of memory alignment.
> 4) if hotplug advice: lesser of advice and end of memory alignment.
>
> Suggested-by: David Hildenbrand <david@xxxxxxxxxx>
> Signed-off-by: Gregory Price <gourry@xxxxxxxxxx>
> Acked-by: David Hildenbrand <david@xxxxxxxxxx>
Acked-by: Mike Rapoport (Microsoft) <rppt@xxxxxxxxxx>
> ---
> arch/x86/mm/init_64.c | 15 ++++++++++-----
> 1 file changed, 10 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
> index ff253648706f..f1a495e998ce 100644
> --- a/arch/x86/mm/init_64.c
> +++ b/arch/x86/mm/init_64.c
> @@ -1452,16 +1452,21 @@ static unsigned long probe_memory_block_size(void)
> }
>
> /*
> - * Use max block size to minimize overhead on bare metal, where
> - * alignment for memory hotplug isn't a concern.
> + * When hotplug alignment is not a concern, maximize blocksize
> + * to minimize overhead. Otherwise, align to the lesser of advice
> + * alignment and end of memory alignment.
> */
> - if (!boot_cpu_has(X86_FEATURE_HYPERVISOR)) {
> + bz = memory_block_advised_max_size();
> + if (!bz) {
> bz = MAX_BLOCK_SIZE;
> - goto done;
> + if (!boot_cpu_has(X86_FEATURE_HYPERVISOR))
> + goto done;
> + } else {
> + bz = max(min(bz, MAX_BLOCK_SIZE), MIN_MEMORY_BLOCK_SIZE);
> }
>
> /* Find the largest allowed block size that aligns to memory end */
> - for (bz = MAX_BLOCK_SIZE; bz > MIN_MEMORY_BLOCK_SIZE; bz >>= 1) {
> + for (; bz > MIN_MEMORY_BLOCK_SIZE; bz >>= 1) {
> if (IS_ALIGNED(boot_mem_end, bz))
> break;
> }
> --
> 2.43.0
>
--
Sincerely yours,
Mike.
